KVM: SEV: WARN if SEV-ES is marked active but SEV is not

WARN if the VM is tagged as SEV-ES but not SEV.  KVM relies on SEV and
SEV-ES being set atomically, and guards common flows with "is SEV", i.e.
observing SEV-ES without SEV means KVM has a fatal bug.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211109215101.2211373-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.h

@@ -242,7 +242,7 @@ static inline bool sev_es_guest(struct kvm *kvm)
 #ifdef CONFIG_KVM_AMD_SEV
 	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
 
-	return sev_guest(kvm) && sev->es_active;
+	return sev->es_active && !WARN_ON_ONCE(!sev->active);
 #else
 	return false;
 #endif